The formation of mesostructured hexagonal alumina from aluminum nitrate in micellar solutions of sodium dodecyl sulfate (SDS) in a water/urea mixture as reported by Yada et al. (Inorg. Chem. 1997, 36, 5565) has been investigated by means of fluorescence probing (spectrofluorometry and time-resolved fluorescence), using pyrene and dipyrenylpropane as fluorescent probes. The investigations involved mainly the reference systems 0.60 M SDS and 0.60 M SDS/9.1 M urea, and the precursor system 0.60 M SDS/9.1 M urea/0.30 M Al(NO3)(3), at a temperature of 60 degreesC. In a first step, the micelle aggregation number, the micelle microviscosity, and the pyrene fluorescence lifetime were determined in the initial state of these systems, i.e., before the start of the polymerization process that leads to the mesotructured material. The effects of substitution of Al(NO3)(3) by AlCl3 or NaNO3 and of a change of the concentrations of SDS and Al(NO3)(3) were also investigated. The micelles present in the precursor system were found to have an aggregation number of 105, which indicated a slightly elongated shape, and an ionization degree around 0.12, indicating a strong binding of Al3+ ions to the micelle surface. The bound Al3+ ions were shown to carry to the micelle surface a small amount of nitrate ions, to the extent of about 5 mol % with respect to SDS. The bound nitrate ions strongly quenched the pyrene fluorescence. Similar results were obtained for the dilute precursor system 0.10 M SDS/9.1 M urea/0.30 M Al(NO3)(3) and for the corresponding reference systems. In a second step the systems were studied as a function of the aging time (time spent at 60 degreesC). The microviscosity of the micelles in the precursor system increased with the aging time. This result, together with the variation of the time after which a precipitate was visually observed in the system with the SDS concentration, strongly supports a mechanism where the main locus for polymerization is the micelle surface. The pyrene lifetime increased with the aging time revealing a release of nitrate ions that is associated to the polymerization of the bound aluminum species that decreases their electrical charge. However the micelle aggregation number remained unaffected by the polymerization. It appears that the transformation of the complex formed by the growing alumina polymers and the dodecyl sulfate micelles into an organized material takes place just before or during the precipitation of the organized solid. This behavior is similar to that noted for the formation of organized mesoporous silica even though qualitative differences exist in the precursor systems for silica and alumina used in our investigations. A model is presented that explains the various observations.